docs fixes (#354)

## Available PR templates

<!--
Github doesn't allow PR template selection the same way that it is
possible with issues.
  Preview this and select the appropriate template
-->

- [Default](?expand=1&template=default.md)
- [Version Release](?expand=1&template=version_release.md)
- _Alternatively delete and start empty_

mkdocs.yml

@@ -60,6 +60,7 @@ nav:
       - ecosystem/index.md
       - ecosystem/geoarrow.md
       - ecosystem/geopandas.md
+      - ecosystem/jupyter-widgets.md
       - ecosystem/panel.md
       - ecosystem/shiny.md